Manual Pages  — IICBUS

iicbus – I2C bus system

SYNOPSIS DESCRIPTION I2C DEVICES INTERFACES BUS FREQUENCY CONFIGURATION Device Hints Flattened Device Tree Data Sysctl and Tunable SEE ALSO HISTORY AUTHORS

device iicbus device iicbb

device iic device ic device iicsmb

The iicbus system provides a uniform, modular and architecture-independent system for the implementation of drivers to control various I2C devices and to utilize different I2C controllers.

I2C is an acronym for Inter Integrated Circuit bus. The I2C bus was developed in the early 1980's by Philips semiconductors. Its purpose was to provide an easy way to connect a CPU to peripheral chips in a TV-set.

The BUS physically consists of 2 active wires and a ground connection. The active wires, SDA and SCL, are both bidirectional. Where SDA is the Serial DAta line and SCL is the Serial CLock line.

Every component hooked up to the bus has its own unique address whether it is a CPU, LCD driver, memory, or complex function chip. Each of these chips can act as a receiver and/or transmitter depending on its functionality. Obviously an LCD driver is only a receiver, while a memory or I/O chip can both be transmitter and receiver. Furthermore there may be one or more BUS MASTERs.

The BUS MASTER is the chip issuing the commands on the BUS. In the I2C protocol specification it is stated that the IC that initiates a data transfer on the bus is considered the BUS MASTER. At that time all the others are regarded to as the BUS SLAVEs. As mentioned before, the IC bus is a Multi-MASTER BUS. This means that more than one IC capable of initiating data transfer can be connected to it.

Some I2C device drivers are available:

Devices	Description
iic	general i/o operation
ic	network IP interface
iicsmb	I2C to SMB software bridge

The I2C protocol may be implemented by hardware or software. Software interfaces rely on very simple hardware, usually two lines twiddled by 2 registers. Hardware interfaces are more intelligent and receive 8-bit characters they write to the bus according to the I2C protocol.

I2C interfaces may act on the bus as slave devices, allowing spontaneous bidirectional communications, thanks to the multi-master capabilities of the I2C protocol.

Some I2C interfaces are available:

Interface	Description
pcf	Philips PCF8584 master/slave interface
iicbb	generic bit-banging master-only driver
lpbb	parallel port specific bit-banging interface
bktr	Brooktree848 video chipset, hardware and software master-only interface

Set hint.iicbus.%d.frequency to the frequency in Hz, on systems that use device hints to configure I2C devices. The hint is also honored by systems that use FDT data if no frequency is configured using FDT.

Configure the I2C bus speed using the FDT standard clock-frequency property of the node describing the I2C controller hardware.

The iicbus manual page first appeared in FreeBSD 3.0 .

This manual page was written by Nicolas Souchu.